We are using a whole muscle transplantation technique either with denervation of the muscle 3 to 4 weeks before transplantation (pre-denervated transplant) or with denervation at the time of transplantation (normal transplant). The muscle is removed completely and either returned to the same site (orthotopic autograft) or returned to a different site (heterotopic autograft). In each case, the skeletal muscle fibers degenerate and then regenerate as the transplanted muscle is revascularized and reinnervated. In the cat, it takes approximately a year for the transplant to stabilize. Our goal is to determine the degree of restoration of control structure and function obtained in stabilized extensor digitorum longus muscles of cats transplanted orthotopically or heterotopically and with or without pre-denervation of the muscle. Control values are for non-denervated and non-transplanted extensor digitorum longus muscles of cats of comparable body mass. We will use a broad range of histological, histochemical, biochemical, and physiological measurements of structure and function to describe the degree of restoration. Functional measurements include contractile properties; blood flow, and oxygen consumption from rest up to maximum work; and electromyography during locomotion. From the descriptive data we will formulate and test hypotheses as to the biological mechanisms involved. This will enable us to characterize the role of mass, fiber geometry, graft site, and pre-denervation on stabilized transplants. These factors are necessary for the selection of appropriate muscles for transplantation in the clinical treatment of muscle paralysis due to disease or trauma.